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From: "fabio de francesco" <fmdf@tiscali.it>
Newsgroups: comp.lang.ada
Subject: Re: "new" word
Date: 16 Mar 2005 04:53:41 -0800
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Larry Kilgallen wrote:
> In article <1110966980.482176.111570@f14g2000cwb.googlegroups.com>,
"fabio de francesco" <fmdf@tiscali.it> writes:
> > Ciao,
> >
> > While reading "the big online book of Linux Ada programming", by
Ken O.
> > Burtch, I stopped at the following assertion
> > (http://www.pegasoft.ca/resources/boblap/13.html):
> >
> > "Usually you allocate memory with the Ada new statement. Where does
new
> > get its memory? It uses the standard C library's malloc function."
> >
> > Does really Ada use Libc to implement "new"? Is it true?
>
> Of course not.  Ada is a language standard, and allocates memory out
of
> thin air.  That memory has no physical reality and costs nothing. It
is
> unlimited in size.

Your sarcasm is totally inopportune. Maybe you don't even know the
difference between what is provided by the OS and what comes from the
Standard C Library.

Standard C Library provides memory to C user programs through asking
pages to the kernel, that is malloc -> brk -> (assembly code) int h80
-> sys_brk(C code in kernel).

So what forbids to whichever Ada implementation to directly ask memory
to the kernel the same way LibC does?

> Some particular Ada _implementation_ however, has to deal with
physical
> memory.  It is possible that some implementation might be layered on
top
> of the C memory allocation facilities.
>
> > It seems absurd to me. I don't understand why Ada should depend on
a C
> > standard library.
>
> Some operating systems are very C-centric in their operating system
calls,
> and without direct experience I would say that Linux is likely one of
them.
> I have seen "portable" C programs which spend half of their lines of
code
> rolling their own version of facilities that are built into other
operating
> systems.

What has it got to do with the question? While kernel is written with
C, if you want to use a syscall from user space you have to issue a
software interrupt in a standardised way (see syscalln() macros) to
access kernel space. So what would prevent an Ada implementation to
call sys_brk using the very same technique? In theory Ada
implementation doesn't need LibC, it only need to access kernel.

Ciao,

fabio de francesco